After the change, with two experience heirlooms, the ST quests reward a little under 8000 xp. Quests in Swamp of Sorrows with experience heirlooms reward almost 9000 xp.
In retrospect it's a bit more than a third of the previous experience, probably somewhere around 40-45%.
It's a little sad that they reduced it below what a normal quest would be. I actually expected it to be a little higher than a normal quest reward.